Question

How the Discrete Cosine Transformation is applied for JPEG image compression. Do intensive
literature survey and explain in detail

Answer 1

Discrete Cosine Transformation is applied for JPEG image compression

Discrete Cosine Transformation:

A Discrete Cosine Transformation (DCT) expresses a finite sequence of data points in terms of a sum of cosine functions oscillating at different frequencies. The DCT,first proposed by Nasir Ahmed in 1972,is a widely used transformation technique in signal processing and data compression. It is used is most digital media,including digital images (such as JPEG and HELF,where small high-frequency components can be discarded),digital video (such as MPEG and H,26X), digital audio (such as Dolby Digital,MP3 and AAC),digital television (such as SDTV,HDTV, and VOD),digital radio( such as AAC+ andDAB+).

DCTS are also important to numerous other applications in science and engineering,such as digital signal processing,telecommunication devices,reducing network bandwidth usage and spectral methods for the numerical transformation.

JPEG image compression:

JPEG stand for Joint Photographic Experts Group,which was a group of image processing experts that devised a standard for compressing images(ISO). This is the image compression alogrithm that most people mean when they say JPEG compression,and the one that we will be describing in this class

The Process:

The following is a general overview of the JPEG process. Later,we will take the reader through a detailed tour of JPEG'S method so that a more comprehensive understanding of the process may be acquired.

1. The image is broken into 8*8 blocks of pixels.

2. Working from left to right,top to bottom,the DCT is applied to each block.

3. Each block is compressed through quantization.

4. The array of compressed blocks that constitute the image is stored in a drastically reduced amount of space.

5. When desired the image is reconstructed through decompression, a process that uses the Inverse Discrete Cosine Transformation (IDCT).

Lossy and lossless image compression:

• Transform coding – This is the most commonly used method. Discrete Cosine Transform (DCT) – The most widely used form of lossy compression. ...
• Reducing the color space to the most common colors in the image. ...
• Chroma subsampling. ...
• Fractal compression.